My Phantom has always been reasonably well behaved, especially after converting it to a P1.5 (in a P2 shell). Things went very sour, however, when I tried to fly waypoints using the iPad Ground Station. I've posted about this before, how the Phantom would stray from the programmed flight path, wander around in circles at waypoints and even head off in seemingly random directions. On at least three occasions I came close to losing the Phantom among the trees and wetlands that surround us. To make a sad story short, the problem turned out to be the need to adjust the compass to compensate for the magnetic declination, which is 16 degrees from true north where I live, near Seattle. To do this I just loosened the screws on the compass and twisted it to the right about 16 degrees, with the Phantom facing away from me. (I'm not sure if this is how you'd do the adjustment elsewhere, so ask an expert before you make any risky flights.) I then did an advanced calibration using the NAZA Assistant and a "compass dance" calibration before flying. The results were a dramatic improvement. I've flown two simple waypoint missions so far and the Phantom hasn't strayed from the flight path or the waypoints. As a bonus, the quad now holds a GPS hover like a rock. There are members here who understand the technical aspects of this far better than me, so if you have questions about fine-tuning, I'm not the person to ask -- but I do encourage you to consider adjusting the compass as a precaution, especially if your Phantom isn't flying as well as you expected when controlled by the Ground Station.